1. Field of the Invention
The present invention relates to a thermally-assisted magnetic recording head performing recording of information by irradiating a magnetic recording medium with near-field light to reduce an anisotropy field (coercive force) of the magnetic recording medium.
2. Description of the Related Art
In the field of magnetic recording using a magnetic head and a magnetic recording medium, along with the advancement of high recording density of a magnetic disk apparatus, further improvement in the performance of a thin film magnetic head and a magnetic recording medium is demanded. As the thin film magnetic head, a composite-type thin film magnetic head is widely used having a structure in which a magnetoresistive (MR) element for reading and an induction-type electromagnetic transducer element (magnetic recording element) are laminated on a substrate. In the magnetic disk apparatus, the thin film magnetic head is provided in a slider that flies slightly above a surface of the magnetic recording medium.
In such a magnetic recording device, along with the advancement of high density in magnetic recording, so-called thermally-assisted magnetic recording is proposed in which a magnetic material with large magnetic anisotropy energy Ku is used as the recording medium, and a magnetic field is applied to perform writing after the coercive force is reduced by applying heat to the magnetic recording medium. In the thermally-assisted magnetic recording, methods in which laser light is used in order to apply heat to the magnetic recording medium are common. Among such methods, there is a method (near-field light heating) in which the laser light is converted to near-field light and in which the magnetic recording medium is heated by irradiating the magnetic recording medium with the near-field light. The near-field light is a kind of electromagnetic field that is formed around a substance and has a property that a diffraction limit due to the wavelength of the light can be ignored. By irradiating a microstructure body with light having aligned wavelengths, near-field light that depends on the scale of the microstructure body is generated, and focusing of the light to a minimum region of about several tens of nm is possible.
A specific configuration of a near-field light probe that generates near-field light is disclosed in JP2001-255254A and JP2003-114184A. The near-field light probe disclosed in JP2001-255254A and JP2003-114184A has a metallic scatter of a shape of a conical body, a triangle and the like. When light is incident onto the scatter of the near-field light probe, near-field light is generated at a vertex portion of the scatter. In a case where such a near-field light probe is used in thermally-assisted magnetic recording, the near-field light probe is arranged in the magnetic recording head in such a manner that the vertex of the scatter is positioned on an air bearing surface (ABS) opposing the recording medium. The scatter is irradiated with light from an opposite side of the ABS, and near-field light is radiated from the vertex of the scatter toward the recording medium. Such a near-field light probe is referred to as a plasmon antenna.
However, in a method in which the plasmon antenna is directly irradiated with light as described above, the efficiency of converting the light radiated onto the plasmon antenna to the near-field light is low. Most of the energy of the light radiated onto the plasmon antenna is reflected at the surface of the plasmon antenna or converted into heat. The vertex (near-field light generator) of the plasmon antenna is formed to have a dimension smaller than the wavelength of the light. Therefore, the volume of the plasmon antenna is small. Thus, in the plasmon antenna, temperature rise accompanying the conversion of the energy of the incident light to heat is very large. Due to this temperature rise, the plasmon antenna causes volume expansion. If such a plasmon antenna is arranged on the ABS of the thermally-assisted magnetic recording head that opposes the magnetic recording medium, the plasmon antenna protrudes from the ABS due to the volume expansion. In order to prevent the magnetic recording head from contacting the magnetic recording medium during the expansion, an end part of the MR element positioned on the ABS is kept far away from the magnetic recording medium. As a result, a problem occurs that, for example, signals recorded in the magnetic recording medium cannot be read during a recording operation, which impairs the reliability of the recording head. Further, when heat generation is large, problems occur, such as breakage (e.g., melting) of the plasmon antenna, degradation in performance (heating capability) that accompanies deformation due to migration of the material that configures the plasmon antenna, and damage to the magnetic recording medium.
Therefore, thermally-assisted magnetic recording heads using surface plasmon are proposed in JP2005-116155A and JP2012-22768A. In these thermally-assisted magnetic recording heads, instead of being directly radiated to the plasmon antenna, propagation light that propagates through a waveguide couples with the plasmon generator in a surface plasmon mode via a cladding layer. The light propagating through the waveguide is totally reflected at an interface between the waveguide and the cladding layer. In this case, light that is referred to as evanescent light and that exudes to the cladding layer is generated. The evanescent light and collective oscillations of electric charges in the plasmon generator are coupled, and surface plasmons are excited in the plasmon generator. The excited surface plasmons propagate to a near-field light generation end surface that is an ABS side end part of the plasmon generator, and near-field light is generated at the near-field light generation end surface.
However, even for a thermally-assisted magnetic recording head using the surface plasmons, temperature rise to some extent in the plasmon generator onto which the light is focused cannot be avoided, and additional measures are required to prevent overheating. To prevent overheating in the plasmon generator, it is effective that a structure body having a large volume is provided in contact with the plasmon generator or is integrally provided with the plasmon generator to function as a heat sink. Because the structure body is in contact with the plasmon generator or is integrated with the plasmon generator, the structural body must be made of a material (specifically, noble metal such as Au and Ag that can be used as the material of the plasmon generator) that does not interfere with the generation of the near-field light. From a point of view of heat dissipation efficiency, it is preferable that the structure body be exposed on the ABS. However, in practice, it is difficult to expose the structure body on the ABS due to an influence on the near-field light and a problem when processing the slider.
Further, a main magnetic pole for applying a writing magnetic field to the recording medium is provided above the plasmon generator. A separator layer that does not absorb much of the near-field light is provided between the near-field light generation end surface, which is the ABS side end part of the plasmon generator, and the main magnetic pole.